1. Field of the Invention
This invention relates to an insulating composition, more particularly, to a preformed composite laminate insulating body formed of layers of cellular ceramic or siliceous material adhesively secured to a layer of reinforcing material.
2. Description of the Prior Art
Various insulation materials have been used in the past for preventive flow of heat to or from an insulated body. Special problems are encountered when the heat source is kept in the temperature range 800.degree. to 1500.degree.F. as is common in steam pipes. In this temperature range, conventional insulating materials, such as wood or cork, are ineffective.
Composite insulating materials have been suggested to overcome the difficulties of providing an insulating material which retains its insulating ability when subjected to temperatures in the range 800.degree. to 1500.degree.F. Positioning a thermoplastic structure surrounded by a rigid foam around a pipe, then passing a heated fluid through the pipe to melt the thermoplastic and providing an air plenum surrounding the pipe is disclosed in U.S. Pat. No. 3,418,399. A core of cellular material such as a cellular glass, encased by a skin of high temperature resinous material may be used to insulate a pipe, as taught in U.S. Pat. No. 3,157,204.
When composite insulating materials are subjected to temperatures in the range 800.degree. to 1500.degree.F., small cracks or fissures form in the cellular insulating layer adjacent the heat source. The cracks permit heat to flow with decreased resistance through this first layer of insulation, thus decreasing the insulating ability of the composite material. When excessive thermal stress is encountered, e.g., exposure to very high temperatures or to cyclic heating between low and high temperatures, the insulating layer adjacent the heat source may fracture into small sections. Stresses then develop within the layer of insulating material adjacent the fractured layer due to increased heat transfer through the inner layer and the resultant stresses are sufficient to propagate fracture or deformation of the second layer of the composite material, with further reduction of insulating efficiency.
It is known to form an insulating material comprising a plurality of alternate layers of thin precracked ceramic materials, as taught in U.S. Pat. No. 3,528,400. The ceramic body is formed by building up alternate single thicknesses of two desired ceramic compositions, drying each layer, and firing the composite. Although the article thus formed is capable of resisting body deformation caused by thermal stresses from temperatures to 1800.degree.F., the complicated procedure required to form such a material limits its application.
This invention provides an improved composite laminate insulating material which maintains its integrity and insulating ability even when the inner layer adjacent the heat source and the outer layer develop fractures due to thermal stresses. The invention further provides an economical insulation material of the type described having a long useful life over a temperature range of from 300.degree.F. to 1000.degree.F. Additionally, the invention provides a composite laminate insulating material that may be rapidly and economically fabricated.
Other advantages and details of the invention will be more completely disclosed and described as this specification proceeds.